This invention relates to a deflector for a cathode ray tube (hereinafter called a "CRT"), and more particularly to a stator type deflector in which a plurality of slots for windings are formed in the inner surface of a tubular core and deflecting coils are positioned in these slots.
Most important among the characteristics required for a deflector for a CRT are that both convergence (spot) distortion and raster (pin cushion) distortion are small. This requires making a barrel type magnetic field distribution at the neck of the cathode ray tube, and making a pin cushion type magnetic field distribution at the screen of the tube (see "NHK Technical Journal," Vol. 17, No. 6, 1965). Thus, the windings must be distributed in the barrel pattern at the neck side, and in the pin cushion pattern at the screen side. The conventional CRT deflectors mainly employ the saddle type or the toroidal type that make the manufacture of the windings easy.
Japanese Published Examined Patent Application (JPEPA)57-29825 discloses a toroidal type deflector yoke in which the angle between coils is gradually varied from the neck side to the screen side aling the tube axis to obtained the barrel type magnetic field distribution at the neck and the pin cushion type magnetic field distribution at the screen.
JPEPA 57-40621 discloses a saddle-toroidal type deflector yoke in which the angle of winding width of a vertical toroidal coil at the screen side viewed from the tube axis is made smaller than that at the neck side viewed from the tube axis to cause a pin cushion magnetic field at the screen side and a barrel magnetic field at the neck side.
However, the saddle type deflector yoke and the toroidal type deflector yoke have poor efficiency because of a poor degree of coupling, and a large core diameter or large dielectric loss, and cause the problem of much heat being generated if they are used for a CRT that has a high horizontal deflection frequency (e.g. for CAD/CAM or text files). In addition, because recent CRT displays are required to have smaller packages, wide angle deflection (such as 100 degree deflection) causes a serious problem in improving the efficiency of the deflector yoke.
Japanese Published Examined Utility Model Application (JPEUMA) 59-24118 (Japanese Patent Application 52-41952) discloses a stator type deflector in which a plurality of grooves are formed in the inner surface of a tubular (horn-shaped) magnetic core along the axis of a cathode ray tube. Horizontal and vertical deflecting coils are wound in such a manner that they are engaged in these grooves. Because the horizontal and the vertical deflecting coils are engaged in the grooves, the deflector can cause the inner surfaces of the coils to be as close to the outer surface of the cathode ray tube as possible so that the deflection efficiency can be improved.
Japanese Published Unexamined Utility Model Application (JPUUMA) 61-114754 [Japanese Utility Model Application (JUMA) 59-196942] discloses a stator type deflector in which the spot and the raster distortions are reduced by forming Y-shaped winding paths, which extend from an end with a smaller opening to the other end with a larger opening and which are bifurcated in the middle, on a funnel-shaped inner periphery, the inner diameter of which expands along the axis.
JPUUMA 57-29238 (JUMA 57-163259) also discloses a staor type deflector with high deflection efficiency. FIG. 10 shows a core used for the deflector disclosed in the specification, while FIG. 11 shows a stator where coils are wound on the core of FIG. 10. Referring to these figures, core 700 has winding slots 700a, 700b, 700c and 700d in which vertical deflection coil 800 is provided, and winding slots 700e, 700f, 700g and 700h in which horizontal deflection coil 900 is provided. Winding slots 700a, 700b, 700c and 700d are radially formed around the tube axis. Winding slots 700e, 700f, 700g and 700h are formed in such a manner that the first angle in the plane normal to the tube axis at the neck side between first line 300n connecting the tube axis to the center of the winding slot in the transverse direction and horizontal reference line 300 (.theta.ni for slot 700h) is larger than an angle in the plane normal to the tube axis as the screen side between second line 300s connecting the tube axis to the center of the winding slot in the transverse direction and horizontal reference line 300 (.theta.si for slot 700h). This makes the horizontal deflection distribution a pin cushion magnetic field.
The deflector yoke disclosed in JPEPA 57-29825 has toroidal windings, and has poor deflection efficiency as described. It also requires a special technique for fastening the windings by some means, so that it is difficult to obtain products with uniform quality in mass production.
The deflector yoke disclosed in JPEPA 57-40621 tends to improve mechanical stability when a toroidal coil is diagonally wound around a core. However, although it has the effect of reducing the amount of displacement of the winding from an intended position in winding conductors and after completion of winding of the conductors, dispersion may be caused in the distribution of the magnetic field depending on the accuracy of the winding. In addition, it is necessary to fix the conductors in the desired position with adhesives or the like after completion of the winding. Furthermore, because the deflector yoke is a toroidal type, it has poor deflection efficiency as described.
In the deflector disclosed in JPEUMA 59-24118, because the grooves wound with the deflecting coils are radially formed around the tube axis, it is impossible to vary the winding distribution at the neck side from that at the screen side by only the windings in the grooves, and the convergence distortion becomes large if the raster distortion is intended to be lowered, so that it is necessary to provide a separate coil for convergence.
The deflector disclosed in JPUUMA 61-114754 is difficult to produce because of its complicated structure, and causes substantially fixed winding distribution at the screen side.
In the deflector disclosed in JPEUMA 57-29238, because the slots in which the horizontal deflecting coils are positioned differ from those in which the vertical deflecting coils are positioned, the degree of freedom for the winding becomes one half of that for a conventional stator type deflector, in which both the horizontal and the vertical deflecting coils are positioned in all of the slots. Thus, the winding distribution becomes coarse, so that it is not suitable for a CRT with a large deflecting angle because, although desired magnetic field distribution is obtained near the tube axis, the magnetic field is disturbed as the windings become farther away from the tube axis. In addition, because the slots in which the vertical deflecting coils are positioned are formed along radial lines from the tube axis, the vertical winding distribution at the neck side cannot be varied from that at the screen side, so that it is impossible to make the vertical deflection magnetic field have a barrel distribution at the neck side and a pin cushion distribution at the screen side.
Therefore, both the improvement of the convergence at the upper and the lower ends of the screen, and the reduction of the raster distortion in the transverse direction cannot be accomplished. Thus, it is not suitable for the vertical type display that is recently being used in large numbers.